So far, a large amount of demolition or construction waste, such as e.g. hardened concrete or mortar, is disposed in landfills and minor quantities are partially reused as raw material for low-tech applications in the construction industry.
Current practice is that demolition waste material, i.e. concrete, is crushed and only the coarse fractions are being reused, the smaller ones being discarded due to compromising effect on the properties of fresh and hardened concrete. Therefore, current practice can only be considered incomplete and down-cycling.
However, demolition waste usually comprises significant amounts of useful constituents, e.g. aggregates or binder components, which can in principle completely be recycled and re-used for new construction works. Moreover, in certain regions and countries the disposal of wastes has become more and more expensive and difficult due to new legislations in recent years. In Europe for example, the European directive 2009/98/CE requires a reuse of at least 70 wt.-% of inert demolition waste up to the year 2020. Thus, recycling of demolition or construction waste becomes an important issue in the near future.
Methods for recycling waste concrete or mortar known so far include for example crushing, processing of waste hardened concrete with high performance ultra-sound or sonic impulses, thermal treatment at temperatures above 600° C. or lixiviation with acids. These methods aim in particular at retrieving aggregates.
Also known are clogging treatments which aim at closing pores of the cementitious materials covering the surface of the aggregates in order to improve the quality of the so called recycled concrete aggregates (RCA). Clogging can e.g. be achieved by forming a rim of carbonated cementitious material around the aggregates with the help of carbon dioxide enriched air or by formation of an organic film of polyvinyl acetate (PVA) around the aggregates.
However, these known strategies either require lots of energy, sophisticated equipment or problematic chemicals or the material retrieved is of medium to low quality.
There is thus a need to develop alternative and improved methods which overcome the aforementioned drawbacks and allow retrieving as much of the constituents of demolition waste in best possible quality.